Posted by
ab2tc on
Dec 22, 2011; 10:29pm
URL: http://elecraft.85.s1.nabble.com/K3-LP100A-Dummy-Load-tp7119170p7120191.html
Hi,
I highly recommend the 75W dummy load from Ridge Equipment. I have one permanently connected in my system. I believe it is a military surplus piece of equipment with absolutely superior characteristics like an SWR at 500MHz of 1.05 or less. It has no problem with 100W for a minute or less for sure.
AB2TC - Knut
<quote author="Don Wilhelm-4">
Phil,
All dummy loads are not created equal. Connect yours directly (no coax)
to the LP-100 or an antenna analyzer to determine its characteristics
with frequency (I assume Larry calibrated your LP-100 to NIST
standards). A common ham dummy load is something to tune your amplifier
into and use for general purposes. If you are going to do measurements,
you will need something more like lab quality dummy loads.
Both your dummy load and the 6 feet of RG8X will show a frequency
dependency since you do not have a precision 50 ohm dummy load. A
transmission line that is not terminated in its characteristic impedance
acts like an impedance transformer, and that transformation ratio is
frequency dependent.
If you want a dummy load that is flat WRT frequency and suitable for
instrumentation use, take a look at the Caddock 50 ohm Thick Film
Resistors - they are available up to 100 watt rating. You must use them
on a heat sink, and keep the leads as short as possible, and you will
have a precision dummy load. Caution - even with the heat sink, do not
exceed their power ratings, they will go open circuit in an instant.
I use several of those as instrumentation precision loads.
Other sources of precision dummy loads is Ridge Equipment -
https://www.ridgeequipment.com/store/dummyloads.html. They have one
rated at 75 watts for $12 and one rated at 15 watts for $7.50 - those
are quite good for instrumentation purposes.
73,
Don W3FPR
<snip
</quote>